iPhone users warned over worm that changes wallpaper to Rick Astley picture

Apple's iPhone users have been told to be on the alert as the first worm written to attack their smartphones is reportedly infecting devices in Australia and on the mainland.

At this stage, all the worm appears to do is replace the wallpaper on an infected iPhone with a picture of British pop singer Rick Astley and the message 'ikee is never going to give you up' - a reference to Astley's 1987 hit Never Gonna Give You Up. Users who try to change the wallpaper will find it has returned when their iPhone restarts.

But there was no malicious content and no damage would be done to infected iPhones, said Chia Wing Fei, senior response manager of F-Secure Labs, which handles the latest online security news from around the world.

Chia said the malicious code would only run on devices that had been unlocked. A lot of iPhone users in Hong Kong would have to unlock their phones to download software from sources other than iTunes. Those who bought parallel-imported phones from the US would also need to unlock the phones to use them in Hong Kong.

'We have not received any confirmed reports [of infection] in Hong Kong but the author has said it has turned up [on the mainland],' Chia said.

The online magazine PC World reported that the worm was written by Ashley Towns in Australia, who said it was supposed to be a 'small prank'.